1. Field of the Invention
The invention relates to computer networks in general and, in particular, to flow control and congestion management in said networks.
2. Prior Art
The proliferation of computer networks has made network management one of the fastest growing areas of the computer industry. A typical computer network is comprised of some type of communications infrastructure interconnecting a plurality of Personal Computer (PCs) and/or other types of Data Terminal Equipment (DTE). The primary purpose of network management is to design and maintain the network so that it provides optimum service to users of the network.
Flow control and congestion management are factors to be addressed in a well-designed network. If these factors are not properly addressed, the network will not provide optimum service to its users. The expectation for optimum service is even greater as more customer demands for services such as system availability, increased bandwidth, etc., are placed on networks. The prior art has recognized the need for improved services and has provided several teachings regarding flow control and congestion management which will now be addressed.
U.S. Pat. No. 5,280,470 describes bandwidth and congestion management in broadband ISDN networks. The ISDN switch detects the congestion and generates slowdown frames configured in Asynchronous Transfer Mode (ATM) cell format. The cells are sent to slow down selected virtual channels. Even though this type of congestion management appears to work well with ATM protocol, it may not work well with other types of protocol.
U.S. Pat. No. 5,367,523 discloses an Adaptive Rate Base congestion and flow control system wherein rate request and rate response messages are exchanged regularly between data senders and receivers to allow the sender to adjust its data rate to avoid congestion. The frequent exchange of request and response messages tend to consume bandwidth unnecessarily. Consequently, data throughput could be impaired.
U.S. Pat. No. 4,736,369 discloses a technique, termed adaptive session-level pacing, which allows a data receiver to request changing the size of an information window during an active session. The new window size is used in subsequent transfer of information to the data receiver.
U.S. Pat. No. 5,434,860 discloses a flow control methodology in which a data receiver determines a suggested data rate, for a data sender, based in part on a number of data packets lost during a preceding time interval and forwards the suggested rate to the data sender which adjusts its data rate in accordance with the suggested data rate. The technique appears to use higher level software to make the determination.
U.S. Pat. No. 5,455,826 describes a flow control system in which transmitting nodes and receiving nodes are linked together through virtual circuits over a communications link. Each of the virtual circuits are assigned a predetermined amount of bandwidth. If a virtual circuit exceeds its bandwidth allotment, further transmissions on that circuit are disabled for the remainder of the current time period.
PCT published application (Publication Number: WO 95/01029) disclosed a flow control method in which an ATM switch, in an ATM network, determines when the switch is approaching congested states and sets congested indicators provided for in the payload type field of the standard cell format. The receiving port checks the cells and a message is sent to the source port if the proportion of cells carrying the congested indication on a particular channel is relatively high.
IBM® TDB Vol. 38, No. 3 (page 23, August 1995) discloses a flow control method for a CSMA/CD adapter or ethernet adapter wherein buffer overrun is prevented by sending a dummy frame on the link to cause a collision.
The IEEE STD 802.3X proposes a Pause Control MAC Frame for shutting down (i.e. discontinue data transmission) a link if the link becomes congested. The Pause Frame has a field in which the shutdown time is selected by the entity observing the congestion. Among the many drawbacks with this approach is the fact that it cannot be used on links over which information relative to critical applications or functions are to be transmitted because the shutdown time and reporting of results may occur simultaneously and the critical information could be lost or not reported on time. Either way, such results would be undesirable.
Another drawback with 802.3X is that while an entire link is de-activated, queues begin to back-up on stations that need to transmit on the de-activated link. While de-activating, the link relieves congestion for one station, it causes congestion for (possibly many) other stations.
Accordingly, the prior art does not provide an efficient arrangement or mechanism to manage flow control and/or data congestion in a CSMA/CD or ethernet network. It is this problem the present invention addresses.